This invention concerns antioxidants for liquid hydrocarbons, such as petroleum distillates, including fuels. More particularly, this invention relates to such antioxidants which are condensation polymers of certain amino- or thio-alkylene-substituted phenols, lower aliphatic aldehydes, and certain alkylene polyamines.
The catalytic cracking of petroleum to form fuels is a well established method of manufacture. Cracking is the process of converting large hydrocarbon molecules into smaller ones by the application of heat and/or catalysts. However, the products formed by cracking have an undesirable tendency to develop unstable products in many fractions, particularly in the mid-distillate fuels. Under storage and use conditions these products form sludges or gums and also tend to discolor the fuels. The presence of minute quantities of metals such as iron and copper accelerate the degradation process--acting as catalysts in the degradation of hydrocarbons. In order to retard the formation of sludges or gums by degradation, many additives have been proposed which function as stabilizers or antioxidants for the fuel fractions. Other additives are employed as metal deactivators--serving the function of retarding the catalytic effect of metals in the degradation process. One of the requisites for additives for fuels is that they must provide the stabilization, antioxidant properties or metal deactivating properties in very small concentrations in the fuel, so as not to interfere with the performance of the fuels in internal combustion engines.
U.S. Pat. No. 3,269,810 (Chamot Nalco, 1966) discloses a very broad class of structurally related antioxidants/chelants for use in gasolines. While the chelant activity of these materials is good, they are only marginally effective as antioxidants.
Co-pending application Ser. No. 383,941, filed July 21, 1989, titled Antifoulant Compositions and Methods, now U.S. Pat. No. 4,900,427 discloses structurally related refinery antifoulants. These materials also act as antioxidants, but cannot be used as such in sufficient concentration in fuels due to their tendency to cause emulsions when water is present.
Accordingly, it would be desirable to provide an antioxidant for liquid hydrocarbons such as fuels, which would have a high level of antioxidant activity, but not contribute to the formation of emulsions.